On the Average Ultraviolet Emission Line Spectra of High-Redshift Galaxies: Hot and Cold, Carbon-poor, Nitrogen-modest, and Oozing Ionizing Photons
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2024
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| author | Hayes, Matthew J. Saldana-Lopez, Alberto Citro, Annalisa James, Bethan L. Mingozzi, Matilde Scarlata, Claudia Martinez, Zorayda Berg, Danielle A. |
| author_facet | Hayes, Matthew J. Saldana-Lopez, Alberto Citro, Annalisa James, Bethan L. Mingozzi, Matilde Scarlata, Claudia Martinez, Zorayda Berg, Danielle A. |
| contents | We determine the spectroscopic properties of ~1000 ostensibly star-forming galaxies at redshifts (z=4-10) using prism spectroscopy from JWST/NIRSpec. With rest-wavelength coverage between Lya and [S II] in the optical, we stack spectra as a function of nebular conditions, and compare UV spectral properties with stellar age. This reveals UV lines of N III], N IV], C III], C IV, He II, and O III] in the average high-z galaxy. All UV lines are more intense in younger starbursts. We measure electron temperatures from the collisionally excited [O III] line ratios, finding Te=18000-22000 K for the O++ regions. We also detect a significant nebular Balmer Jump from which we estimate only Te=8000-13000 K. Accounting for typical temperature offsets between zones bearing doubly and singly ionized oxygen, these two temperatures remain discrepant by around 40%. We use the [O III] temperatures to estimate abundances of carbon, nitrogen, and oxygen. We find that log(C/O) is consistently ~-1, with no evolution of C/O with metallicity or stellar age. The average spectra are mildly enhanced in Nitrogen, with higher N/O than low-z starbursts, but are less enhanced than samples of high-z galaxies with visible UV N III] and N IV]. Whatever processes produce the N-enhancement in the individual galaxies must also be ongoing, at lower levels, in the median galaxy in the early Universe. The strongest starbursts are a source of significant ionizing emission: ionizing photon production efficiencies reach 10^25.7 Hz/erg, and show multiple signatures of high Lyman continuum escape, including Mg II escape fractions nearing 100%, significant deficits in [S II] emission, high degrees of ionization, and blue UV colors. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2411_09262 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | On the Average Ultraviolet Emission Line Spectra of High-Redshift Galaxies: Hot and Cold, Carbon-poor, Nitrogen-modest, and Oozing Ionizing Photons Hayes, Matthew J. Saldana-Lopez, Alberto Citro, Annalisa James, Bethan L. Mingozzi, Matilde Scarlata, Claudia Martinez, Zorayda Berg, Danielle A. Astrophysics of Galaxies We determine the spectroscopic properties of ~1000 ostensibly star-forming galaxies at redshifts (z=4-10) using prism spectroscopy from JWST/NIRSpec. With rest-wavelength coverage between Lya and [S II] in the optical, we stack spectra as a function of nebular conditions, and compare UV spectral properties with stellar age. This reveals UV lines of N III], N IV], C III], C IV, He II, and O III] in the average high-z galaxy. All UV lines are more intense in younger starbursts. We measure electron temperatures from the collisionally excited [O III] line ratios, finding Te=18000-22000 K for the O++ regions. We also detect a significant nebular Balmer Jump from which we estimate only Te=8000-13000 K. Accounting for typical temperature offsets between zones bearing doubly and singly ionized oxygen, these two temperatures remain discrepant by around 40%. We use the [O III] temperatures to estimate abundances of carbon, nitrogen, and oxygen. We find that log(C/O) is consistently ~-1, with no evolution of C/O with metallicity or stellar age. The average spectra are mildly enhanced in Nitrogen, with higher N/O than low-z starbursts, but are less enhanced than samples of high-z galaxies with visible UV N III] and N IV]. Whatever processes produce the N-enhancement in the individual galaxies must also be ongoing, at lower levels, in the median galaxy in the early Universe. The strongest starbursts are a source of significant ionizing emission: ionizing photon production efficiencies reach 10^25.7 Hz/erg, and show multiple signatures of high Lyman continuum escape, including Mg II escape fractions nearing 100%, significant deficits in [S II] emission, high degrees of ionization, and blue UV colors. |
| title | On the Average Ultraviolet Emission Line Spectra of High-Redshift Galaxies: Hot and Cold, Carbon-poor, Nitrogen-modest, and Oozing Ionizing Photons |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2411.09262 |